1. Field of the Invention
This invention relates generally to a process for making acrylic coating resins and more specifically to superior solvent blends useful in the synthesis of acrylic high solids coating resins.
2. Description of the Prior Art
A large variety of acrylic coating compositions are known. Low solids coatings, i.e., those containing about 18 to 40 wt.% solids and the balance solvents, have heretofore been developed in which the resins themselves are characterized by high molecular weights, e.g., molecular weights in the range of 20,000 to 40,000. Such high solvent concentrations are required with these high molecular weight resins in order to supply flowability and other properties necessary for ease in applying a uniform coating. Due to strict air pollution regulations, pollution abatement of solvents is of paramount importance. To this end, the industry has expended much effort in attempting to develop high solids coatings, that is, coatings having low molecular weight resins (e.g., from about 1,000 to 6,000 molecular weight) in order to reduce the amount of solvents necessary in the blend for coating applications and, hence, the pollution difficulties associated with the solvents themselves. These high solids acrylic coatings are useful as exterior finish for automobiles, trucks, airplanes and as an appliance finish.
Illustrative of prior art, high solids acrylic resins are those disclosed in U.S. Pat. No. 4,276,212 and in European patent application Nos. 27,719; 29,339; 29,594 and 29,683.
The prior art has employed a variety of solvents in the preparation of their high solids coatings and it is desirable to employ the same solvent both as the polymerization solvent and as the coating solvent to avoid the need to remove a polymerization solvent before formulating the high solids coatings from a polymerized resin.
Solvents which are indicated to be typical in these references (e.g., those mentioned in European patent application No. 29,594) are: toluene, xylene, butyl acetate, acetone, methyl isobutyl ketone, methyl amyl ketone, methyl ethyl ketone, butyl alcohol and other aliphatic, cycloaliphatic and aromatic hydrocarbons, esters, ethers, ketones, and alcohols.